It is necessary to protect integrated circuitry from environmental damage. This is usually done by encapsulation. It is well known in liquid crystal display (LCD) applications that the drive circuits are being placed physically on the liquid crystal display substrates along with the LCD circuit to reduce the number of interconnections and the cost. When these elongated active circuits are placed upon the substrate of the liquid crystal display, stress generated by encapsulation materials and processes may cause cracking or damage to the underlying substrate.
The substrates may be of a type such as glass, ceramic, silicon and the like. Even though the integrated circuits on the substrates are protected by a layer of passivation such as silicon dioxide or silicon nitride, moisture can penetrate through the passivation barrier gradually over a period of time. This can cause high leakage current and leads to performance degradation. Hence, adequate protection of these circuits on a substrate with encapsulation is necessary for a reliable display. It would be advantageous to provide some method and apparatus that not only protected the circuitry but also did not damage the underlying substrate.
Good encapsulation material of a circuit on a substrate such as glass has several requirements. First, the materials should have good adhesion to the substrate. Second, the coefficient of thermal expansion should be close to the underlying substrate. Third, the material should have a low curing temperature, preferably less than 100.degree. C. Fourth, it should have a low alkaline content. Fifth, it must be resistive to moisture attack. Sixth, it must have provided low stress to the underlying circuitry.
It is very difficult for a commercially available encapsulation material to satisfy all of these demands.
The conventional LCD panel packaging is shown in FIG. 1 and is designated generally by the numeral 10. Driver circuit 11 is on substrate 13, which may be a substrate such as glass, and is adjacent the upper substrate 14 which is spaced from the lower substrate 13 and has a well-known seal band 12 between the substrates 13 and 14 to seal the liquid crystal 18 therein between the two substrates 13 and 14 to form a liquid crystal display panel 10. The driver circuit 11 is covered with a protective encapsulation polymer 16 which may be for example Amicon ME1000 which has good adhesion to glass. However, when this material is applied to a glass substrate, such as Corning 7059 glass, with conventional methods, it generally generates cracks in the glass substrate 13. Other encapsulation materials could be used such as Dow Corning JCR 6100 that have low stress applied to the substrate; however, such material delaminates easily from the substrate.
It would be advantageous to encapsulate the integrated driver circuits on a substrate with a protective material in such a way as to not only protect the integrated circuits from environmental damage such as moisture penetration but also to protect the glass substrate from cracking.